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Erschienen in:
2009 | OriginalPaper | Buchkapitel
Collisions and Other Non-random Properties for Step-Reduced SHA-256
verfasst von : Sebastiaan Indesteege, Florian Mendel, Bart Preneel, Christian Rechberger
Erschienen in: Selected Areas in Cryptography
Verlag: Springer Berlin Heidelberg
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We study the security of step-reduced but otherwise unmodified SHA-256. We show the first collision attacks on SHA-256 reduced to 23 and 24 steps with complexities 2
18
and 2
28.5
, respectively. We give example colliding message pairs for 23-step and 24-step SHA-256. The best previous, recently obtained result was a collision attack for up to 22 steps. We extend our attacks to 23 and 24-step reduced SHA-512 with respective complexities of 2
44.9
and 2
53.0
. Additionally, we show non-random behaviour of the SHA-256 compression function in the form of free-start near-collisions for up to 31 steps, which is 6 more steps than the recently obtained non-random behaviour in the form of a semi-free-start near-collision. Even though this represents a step forwards in terms of cryptanalytic techniques, the results do not threaten the security of applications using SHA-256.